1. Field of the Invention
This invention relates to a method for the dissolution of a metal. More particularly, this invention relates to a method for the dissolution of a metal by the contact of the metal with (1) a quaternary ammonium compound and a halogenated hydrocarbon or (2) a quaternary ammonium compound and a halogenated hydrocarbon and a polar solvent.
2. Description of the Prior Art
The dissolution of a metal is an indispensable step for extraction and recovery of the metal from a mixture containing the metal and is extremely important from the industrial point of view. For the dissolution of a metal, a method which comprises dissolving the metal in the aqueous solution of an inorganic acid such as hydrochloric acid has been heretofore employed.
The conventional method for effecting the dissolution of a metal by the use of an inorganic acid has the disadvantages that the inevitable use of a strongly acidic aqueous solution endangers workers handling the solution and gives rise to a large volume of waste water, and that high costs are incurred in the disposal of this waste water.
For solving these problems of the prior art, the present inventors carried out various studies in search of a method for the dissolution of a metal without use of any inorganic acid and consequently invented a method for the dissolution of a metal by the contact of the metal with a halogenated hydrocarbon in the presence of a cationic surfactant. This invention was granted U.S. Pat. No. 4,919,716.
However, this method has the following problems. Since the surfactant has a large molecular weight, the number of mols of the surfactant required for the dissolution is unduly large. Further, the surfactant is generally expensive. After further studies, the inventors have found that numerous metals are dissolved by being brought into contact with a quaternary ammonium compound and a halogenated hydrocarbon or with a quaternary ammonium compound, a halogenated hydrocarbon, and a polar solvent. The present invention has been completed using this knowledge.